A horizontal dipole, that is 1/2 λ long and center fed, would be ideal to use on VHF/UHF. The feed impedance would be in the range to match 50/75 Ω coax. But while it could easily be rotated vertically, there may be issues with trying to bring the coax away from the feedpoint, perpendicular to the antenna element. It would be much simpler if, when rotated vertically, the antenna could be fed from the bottom end. However, the end points of a 1/2 λ antenna present a high impedance and do not match very well to the 50/75 Ω coax very well.

To remidy this, a 1/4 λ matching section is added to the bottom. Tapping a coaxial connector to this 1/4 λ matching section, will then get the 50/75 Ω matching required by the coax.

So the J-Pole is simply a 1/2 λ vertical on the top, (Section A) with a 1/4 λ matching section below (Dection B). The 1/2 λ vertical section is calculated using 468/F (Mhz). The 1/4 λ matching section is calculated using 234/F (Mhz).

To use the calculator, just enter the frequency of interest in the box provided, and then click anywhere on the page. The dimensions for the specified frequency will be displayed on the drawing.

As shown in the drawing, the entire antenna is made from 1/2" rigid copper tubing. There is a copper "T" that connects Sections A, B, and E together and a copper "L" that connects Sections E and D together. All sections are soldered together before final testing. On the top of Section A and Section C there are end caps soldered to the copper tubing. This will help keep out moisture. However, don't put a cap on the bottom. This will allow any condensation to escape. And, because it sort of looks like a cactus, it is often called the Copper Classic.

It has been suggested that a choke be added to the antenna between the coaxial cable feed and the antenna feed. As long as it is within 3 to 4 inches, it should work fine. For 2 Meters, a 4-turn coil of coax, with a diameter of 5 inches, should work fine. If you have some extra length on your coaxial cable feed line, use it for the coil.